1. Field of the Invention
The present invention relates to information transport systems, and more particularly to a link for transporting both data and voice information over a single asynchronous transfer mode system.
2. Description of the Related Art
Transmission systems are employed to transfer or transport information between different locations. Access networks which are presently in use provide asynchronous transfer for either data or voice. Conventional access systems typically include dedicated channels for employing data transfer and different channels for the voice transfer.
Several access network configurations, including fiber-in-the-loop (FITL), employ a host digital terminal (HDT) that interfaces with one or more service networks and serves multiple distant terminals via dedicated transmission links. The distant terminals, which may include, for example, an optical network unit (ONU), hold line cards that connect to each subscriber's dedicated circuit. On the network side of the HDT, services are transported over facilities dedicated to the service type, for example, time division multiplexing (TDM) or asynchronous transfer mode (ATM).
Although the services, including data transfer and voice transfer may share the same physical medium, as in a synchronous optical network (SONET) connection, for example, the services must be carried in separate tributaries, i.e., on separate channels. Between the HDT and the ONU, the two traffic types must share the same medium for economy, for example, the cost of the link is critical for a FITL access network.
Since the services need separate tributaries, conventional systems must predetermine channels for carrying data and predetermine channels for carrying voice transmissions, for example. This limits the available bandwidth to predetermined portions. Data channels cannot be employed for transferring voice and voice channels cannot be employed for transferring data. This results in a bottleneck if more data or more voice information must be transferred than the dedicated channels can accommodate.
Systems for transporting TDM telephony and ATM data in different tributaries of the transmitted signal have suffered several drawbacks. The allocation of bandwidth between the two traffic types is not flexible and the implementation typically leads to separate hardware shelves for each traffic category at each end of the link. Standards for full-service access network describe an all-ATM host terminal to ONU link for passive optical networks (PONs), however the transport of voice services is not well defined and the multi-access functions required a complex control scheme and new devices.
Therefore, a need exists for a system and method which supports high quality voice transmission and data transmission at the rates needed by service categories (e.g., asymmetric digital subscriber line (ADSL), high bit-rate digital subscriber line (HDSL), etc.). A further need exists for a hardware implementation of such a system which employs off-the-shelf components to reduce costs.